The use of compounds having groups of carbazolyl, diphenyl sulfide group, and the like and being connected with an oxime ester structure as photoinitiators has been well known in the art, and the design and the synthesis of novel oxime ester initiators, particularly those having better application performances, are always hot spots in the field of photocuring in recent years. For example, Chinese patent documents having Publication Nos. CN1514845A, CN101508744A, CN101528694A, etc., disclose a variety of oxime ester photoinitiators, and these products have good photosensitivity, storage stability, etc., and satisfy and improve the demand of development of photocurable compositions to some extent.
However, it is found in practical application that there are extremely serious limits for these existing oxime ester photoinitiators in selection of suitable excitation light sources, similarly to conventional photoinitiators. Typically, they can be activated to function only under the irradiation of a broad-spectrum ultraviolet light (UV). Nowadays, light sources for activating photocuring systems (i.e., emitting the broad-spectrum ultraviolet light described above) are mainly high-pressure mercury lamps, and the emission spectra thereof center on 436 nm, 405 nm, 365 nm, 313 nm, and 302 nm, and most of existing photoinitiators have good absorption at the short wavelengths described above. However, such light sources have obvious drawbacks such as large energy consumption, long preheating time, being not environmentally friendly, etc., and they are limited more and more in applications and are being gradually eliminated by the market.
UV-LED light sources have the advantages of high light purity, low energy consumption, simple operation, being environmentally friendly, etc. At present, they have been widely used in fields of civil applications and have been gradually known in the industry of photocuring. Compared to UV mercury lamp systems, UV-LEDs have great advantages in terms of energy saving and emission reduction, improvement of production efficiency, expansion of application range of the photocuring technology, etc. The mode of UV-LED excitation is very promising to become a next mainstream trend of development of the photocuring technology.
Since the UV-LED light source itself has a relatively narrow light emission spectrum, the application performances exhibited by existing photoinitiators under its excitation are hardly satisfactory. Therefore, it is appears to be important to research and develop a photoinitiator having an excellent photosensitive property matched with UV-LED light sources.